not exactly. from the sysread doc:

Returns the number of bytes actually read, 0 at end of file, or undef if there was an error.

this is the full logic, but it can be condensed to fit your needs.

if( defined $read_bytes )
{
  if( $read_bytes >= 0 )
  {
    print 'read something';

    if( $read_bytes == $num_bytes )
    {
      print 'read full buffer';
    }
    elsif( $read_bytes < $num_bytes )
    {
      print 'buffer length: ', $num_bytes, '  read length: ', $read_by
+tes;
    }
    else
    {
      die 'how did i get here?';
    }
  }
  elsif( $read_bytes == 0 )
  {
    print 'EOF';
  }
  else
  {
    die 'how did i get here?';
  }
}
else
{
  die 'error reading socket';
}
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